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Jason DavisAugust 12, 2019

Hayabusa2 Nailed its Second Touchdown on Asteroid Ryugu

Hayabusa2 successfully touched down on asteroid Ryugu on 11 July, just 60 centimeters away from its aimpoint. JAXA flight controllers had known immediately that the second touchdown had gone according to plan. Now, press materials released 25 July and translated to English on 30 July show just how successful it was. 

You’ve probably seen the stunning touchdown video on social media already, but just in case you haven’t, here it is: 

Hayabusa2 Second Touchdown (short clip)

JAXA

Hayabusa2 Second Touchdown (short clip)
This short clip shows Hayabusa 2's second touchdown, which occurred on 11 July 2019 at 01:06 UTC, as seen from the spacecraft's small monitor camera (CAM-H). The sequence plays at roughly 10 times normal speed. See the full video here.

The video was captured by downward-facing CAM-H, which is mounted on the side of the spacecraft. It’s worth mentioning again that this camera was funded entirely by public donations!

Just like the first touchdown, Hayabusa2’s firing of a tantalum bullet as the sample horn smooshed into the surface sprayed a lot of surface material into the air. On the first touchdown, some of that material stuck to the wide-angle optical navigation camera (ONC-W1) lens, creating permanent cloudy spots in subsequent images. 

When approaching Ryugu’s surface for touchdown, Hayabusa2 relies on a previously dropped target marker to pinpoint the correct landing spot. JAXA flight controllers were concerned that cloudy spots in ONC-W1 images would cause the spacecraft to confuse a bright rock for the target marker.

To mitigate this, JAXA lowered the starting altitude for the final descent from 45 to 30 meters, and implemented some fancy new image processing algorithms to make sure Hayabusa2 would lock onto its target marker correctly. Here is a comparison of the navigation images before and after processing; as you can see, the location of the target marker is much clearer in the processed image.

Hayabusa2 views of second target marker

JAXA

Hayabusa2 views of second target marker
These 2 images of the second target marker Hayabusa2 dropped on Ryugu show 2 different image processing algorithms used by the spacecraft for navigation. The right version uses NBT (Normal Bright object Tracking), while the left is a new technique called DBT (Differential Bright object Tracking).

Hayabusa2 officially touched down on 11 July 2019 at 01:06 UTC, a minute earlier than was initially reported. The touchdown accuracy was astonishing: merely 60 centimeters away from the center of the target zone! Just look at everything Hayabusa2 had to dodge; the area around the touchdown site was littered with rocks about half a meter tall, and roughly 5 meters north of the touchdown zone was a rock 1.4 meters tall. The spacecraft’s sample horn is only a meter long, so an errant touchdown near that rock could have seriously damaged Hayabusa2 and jeopardized getting any samples at all back to Earth. What a good and brave little spacecraft, doing precisely what it was asked to do by its team 244 million kilometers away!

Hazards around Second Hayabusa2 Touchdown Site

JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST

Hazards around Second Hayabusa2 Touchdown Site
These 2 images show the hazards Hayabusa2 had to dodge during its second touchdown. The left image shows the touchdown zone and target marker, while the right shows the height of various rocks and boulders in the region.

Here's another neat view of the sample site, which you may recall is near the artificial crater Hayabusa2 made with an explosion and copper projectile back in April. This view came from 2 cameras as Hayabusa2 descended towards touchdown from a height of about 8 meters. The top view comes from sideways-looking ONC-W2, and the bottom is from downward-looking ONC-W1. The depression in the middle of the top image is the SCI crater. 

Oblique Composite View of Ryugu's Artificial SCI Crater

JAXA, Chiba Institute of Technology, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Meiji University, University of Aizu, AIST

Oblique Composite View of Ryugu's Artificial SCI Crater
This composite view of the region around Ryugu's artificial SCI crater, which is the indentation in the middle of the top image, came from 2 cameras while Hayabusa2 was descending towards its second touchdown at a height of 8 meters on 11 July 2019. The top view is from sideways-looking ONC-W2, and the bottom is from down-looking ONC-W1.

With the second sample safely collected and no further touchdowns planned, operations at Ryugu will now be more subdued. Hayabusa2 may still try to deploy its final rover, MINERVA-II-2, which is believed to be only partially functional. It’s possible the rover will be jettisoned to reduce mass for the return trip, but JAXA officials said they are still finalizing plans.

There isn't another press briefing scheduled until 22 August. Hayabusa2 is scheduled to leave Ryugu in November or December, and return to Earth in late 2020.

Read more: asteroid 162173 Ryugu, Hayabusa2

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Jason Davis

Editorial Director for The Planetary Society
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